Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a fuel vapor canister, and then purge the stored vapors during a subsequent engine operation. The stored vapors may be routed to engine intake for combustion, further improving fuel economy. In a typical canister purge operation, a canister purge valve coupled between the engine intake and the fuel canister is opened, allowing for intake manifold vacuum to be applied to the fuel canister.
Turbocharged and supercharged engines periodically operate with a positive intake manifold pressure. In such scenarios, the canister purge valve must remain closed in order to prevent boost pressure from reaching the fuel vapor canister and desorbing fuel vapor to atmosphere. To prevent boost pressure from forcing open the canister purge valve, a check valve may be disposed between the canister purge valve and the engine intake.
However, during the transition between normal (intake vacuum) engine operating conditions and boosted engine operating conditions, there is a slight lag prior to the check valve closing. As such, the canister purge valve experiences a brief burst of pressure. Over repeated engine transitions, this may cause excessive wear on the canister purge valve membrane, causing the valve to fail prematurely.
Other attempts to address pressurization of the purge passage include dual path-purge systems where a second check valve is coupled to an ejector leading to a passage upstream of an intake air compressor. One example approach is shown by Kempf et al. in U.S. Pat. No. 9,109,550. Therein, during non-boosted conditions, the canister is purged through an open canister purge valve via a first check valve, and during boosted conditions, the canister is purged through an open canister via a second check valve. The additional conduits and check valve allow for dissipation of boost pressure that breaches the first check valve.
However, the inventors herein have recognized potential issues with such systems. As one example, the additional valve, ejectors, conduits, connectors, mounts, etc. add significant manufacturing costs, and require additional testing for undesired emissions and functionality. For engines such as Gasoline Turbocharged Direct Injection (GTDI) engines, the engine operates in non-boosted conditions frequently enough to purge the fuel canister through a single-path purge system that does need the additional purge time during boosted conditions to meet emissions standards. As such, the added expense is unnecessary.
In one example, the issues described above may be addressed by a method for a turbocharged engine, comprising: receiving an indication that the turbocharged engine has transitioned to a boosted mode of operation, and opening a canister purge valve for a pressure relief duration. In this way, pressure from the engine intake is flowed past the canister purge valve, preventing unnecessary wear of the canister purge valve.
As one example, the canister purge valve may be opened until a check valve coupled within a conduit between the canister purge valve and the engine intake closes. The increased airflow through the check valve enables the valve to close faster than if the canister purge valve were closed, thereby developing an upstream backpressure. The method allows for the incorporation of a single check valve within a single-path purge system for a turbocharged engine. In this way, both manufacturing and warranty costs are reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.